Translate virtual address to physical address. See url: https://chyyuu.gitbooks.io/os_course_exercises/content/all/04-1-spoc-discussion.html#虚拟页式存储的地址转换

va2pa.py

# coding: utf-8
#
# This is a solution to
# 	https://chyyuu.gitbooks.io/os_course_exercises/content/all/04-1-spoc-discussion.html#虚拟页式存储的地址转换
#
# Author: github.com/sunskyhsh

import sys

def translate(va, pd):
	print 'Virtual Address 0x%x:'%va
	pdi = (va & 0x7c00) >> 10  # 0111 1100 0000 0000
	pti = (va & 0x03e0) >> 5  # 0000 0011 1110 0000
	offset = va & 0x1f # 0000 0000 0001 1111
	addr = None

	# read page directory entry
	pde = pd[pdi]
	pfn = pde & 0x7f
	valid1 = (pde >> 7)
	print '  --> pde index:0x%x'%pdi,'pde contents:(valid %d, pfn 0x%x)'%(valid1, pde&0x7f)

	# read memory
	with open('memory.txt','r') as f:
		lines = f.readlines()
	if not valid1:
		with open('disk.txt','r') as f:
			print '    --> Fault (page directory entry not valid)'
			exit(1)

	# read page table and page table entry
	line = lines[pfn].split(':')
	pt = map(lambda x: int(x, 16), line[1].split())
	pte = pt[pti]
	pfn = pte & 0x7f
	valid2 = (pte >> 7)
	print '    --> pte index:0x%x'%pti,'pte contents:(valid %d, pfn 0x%x)'%(valid1, pte&0x7f)

	# not valid --> read disk
	if not valid1 and valid2:
		with open('disk.txt','r') as f:
			lines = f.readlines()

	# read value
	line = lines[pfn].split(':')
	value = map(lambda x: int(x, 16), line[1].split())[offset]
	addr = (pfn<<5) + offset # '+' is priorer than '<<'
	if addr:
		if valid1 and valid2:
			print '      --> To Physical address 0x%x'%addr, '--> Value: 0x%x'%value
		else:
			print '      --> To Disk sector address 0x%x'%addr, '--> Value: 0x%x'%value

def main():
	pdb = 0xd80

	# read page directory
	with open('memory.txt','r') as f:
		for line in f.readlines():
			line = line.split(':')
			if int(line[0].split(' ')[1], 16) == (pdb>>5):
				pd = map(lambda x: int(x, 16), line[1].split())
				break

	if len(sys.argv) != 2:
		va =  raw_input('Please input 16 bits address (hexadecimal number): ')
		va = int(va, 16)
	elif len(sys.argv[1]) > 4:
		print 'Error: wrong address.'
		exit(1)
	else:
		va = int(sys.argv[1], 16)
	translate(va, pd)

if __name__ == '__main__':
	main()